What type of algae is this?


New member

I have an algae on my rock that ive been trying to clean. My nitrates were high last week so I did a 40% water change. A week later I'm around 5ppm nitrate.

The algae appears to be bothering my coral and I don't know how to handle it without hurting the coral.

Last week I took each rock out and put it into a 5 gallon bucket of old tank water (during water change) and brushed off with a plastic brush. Then discarded the water and put the rock back in. Some areas near coral I left alone but its covering the rock again.

I've cut my feeding in half this week. It really took off after upgrading from two T5 HO with two deep blue LED strips to a kessil ap700 (75 gallong 4 foot tank). I poured a bag of algagen tisbe pods in too a few weeks ago which the vendor assured me was alive even though I didn't see movement and the bag it looked more brown than green. Maybe this did it?

I should have a hanna phosphate checker come in any day now. I can't make out the salifert phosphate color.

Any idea on the best approach to handle this?

I fed heavier a couple months but didn't notice the algae get bad for a couple months. Started noticing it getting bad 2 weeks ago.

Thank you
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Michael Hoaster

Registered Seaweedist
Premium Member
Filamentous or hair algae. With a bigger tank, I'd recommend a Yellow or Scopas Tang to clean that up. In a 75, they'd likely become tank terrors. Snails are a better option. I'd suggest a variety of reproducing snails, whose population can grow to meet the need. You'll need to still manually remove as much as you can to get it down to the nubs, and the snails will take it from there.


New member
Here are my parameters:

Temp 75F
pH 8/8.2
Phosphate 0.26ppm
Alkalinity 8.8 dKh
Nitrate 2.5/5 ppm
Salinity 1.026
Magnesium 1320 ppm
Calcium 445 ppm

Phosphate looks too high and warrants a water change. However, since it's only been 5 days since my last water change - magnesium and calcium look fine.

Maybe I should add a media bag full of GFO in the sump to try to bring the phosphate down and delay a water change? I also added a little chaeto which I'm not sure if its growing. Its green but isn't changing in size much. Hopefully it's not polluting my tank.

Or maybe I shouldn't add GFO or do a water change and see if the chaeto does anything to my nitrates / phosphates in a couple days?
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Premium Member
If you want to bring your phosphate down that's fine but I wouldn't worry about it too much at the level your tank is at. I prefer tuxedo or royal urchins and thin strip hermits to snails but if you like snails be sure to get types that will reproduce like Micheal Hoaster pointed out. ANd here's a video on using stainless steel straws to remove algae and other "pests". Reef ecosystems are pretty complex, it's a lot more than just chasing nitrates and/or phosphates. While we can only test for dissolved inorganic nitrogen (ammonia, nitrite and nitrate) and dissolved inorganic phosphorus (PO4) the nitrogen cycle on reefs includes dissolved organic nitrogen (amiono acids and urea) and dissolved organic phosphorus as well as particualte forms of nitrogen and phosphrus. Corals are using all these and have prefferences. Add to this corals and algae are manipulating the bacterial and microbial processes and you can see there's quite a bit of guesswork since we can only test for a fraction of what's going on. Here's three videos that might help give a better picture of things:

Forest Rohwer "Coral Reefs in the Microbial Seas"

And "Changing Seas"

Richard Ross What's up with phosphate"

I would encourage you to get Forest ROhwer's "Coral Reefs in the Microbial Seas" (kindle ~$10, papaerback ~$20) It's an excellent introduction to the roles of corals algae and microbes on reefs. And if you want to dig into the research further here's a list of papers:

An Experimental Mesocosm for Longterm Studies of Reef Corals

Phosphate Deficiency:
Nutrient enrichment can increase the susceptibility of reef corals to bleaching:

Ultrastructural Biomarkers in Symbiotic Algae Reflect the Availability of Dissolved Inorganic Nutrients and Particulate Food to the Reef Coral Holobiont:

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates

Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach

High phosphate uptake requirements of the scleractinian coral Stylophora pistillata

Phosphorus metabolism of reef organisms with algal symbionts

Indirect effects of algae on coral: algae‐mediated, microbe‐induced coral mortality
Coral seperated from algae with a .02 µm filter die. Treatment with aampicillan prevents death.

Influence of coral and algal exudates on microbially mediated reef metabolism.
Coral DOC improves oxygen (autotrophy), algae DOC reduces oxygen (heterotrophy).

Effects of Coral Reef Benthic Primary Producers on Dissolved Organic Carbon and Microbial Activity
Algae releases significantly more DOC into the water than coral.

Pathologies and mortality rates caused by organic carbon and nutrient stressors in three Caribbean coral species.
Starch and sugars (doc) caused coral death but not high nitrates, phosphates or ammonium.

Visualization of oxygen distribution patterns caused by coral and algae

Biological oxygen demand optode analysis of coral reef-associated microbial communities exposed to algal exudates
Exposure to exudates derived from turf algae stimulated higher oxygen drawdown by the coral-associated bacteria.

Microbial ecology: Algae feed a shift on coral reefs

Coral and macroalgal exudates vary in neutral sugar composition and differentially enrich reef bacterioplankton lineages.

Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching

Elevated ammonium delays the impairment of the coral-dinoflagellate symbiosis during labile carbon pollution
(here's an argument for maintaining heavy fish loads if you're carbon dosing)

Excess labile carbon promotes the expression of virulence factors in coral reef bacterioplankton

Unseen players shape benthic competition on coral reefs.

Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance.

Macroalgae decrease growth and alter microbial community structure of the reef-building coral, Porites astreoides.

Macroalgal extracts induce bacterial assemblage shifts and sublethal tissue stress in Caribbean corals.

Biophysical and physiological processes causing oxygen loss from coral reefs.

Global microbialization of coral reefs
DDAM Proven

Because sponges are essential players in the carbon, nitrogen and phosphorus cycle(s) on reefs here's some links to research done with them.

Element cycling on tropical coral reefs.
This is Jasper de Geoij's ground breaking research on reef sponges. (The introduction is in Dutch but the content is in English.)

Sponge symbionts and the marine P cycle

Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges
(Chris Kenndall had a problem with low PO4 and had problems raising it with Neophos. Samples sent off showed phosphorus crystals developing in some of the sponges in his system accounting for at least some of his systems consumption.)

Differential recycling of coral and algal dissolved organic matter via the sponge loop.
Sponges treat DOC from algae differently than DOC from corals

Surviving in a Marine Desert The Sponge Loop Retains Resources Within Coral Reefs
Dissolved organic carbon and nitrogen are quickly processed by sponges and released back into the reef food web in hours as carbon and nitrogen rich detritus.

Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)

The Role of Marine Sponges in Carbon and Nitrogen Cycles of COral Reefs and Nearshore Environments.

And since we're discussing favorable and not so favorable bacteria here's a paper looking at how different corals and polyps are influencing the bacteria in the water column.
Aura-biomes are present in the water layer above coral reef benthic macro-organisms


New member
Yes I am using RODI water. Filters were older but I replaced them before the last major water change. So old filters could be a factor.

I tested phosphate again 24 hours later and it increased by 0.03ppm to 0.29ppm. I didn't make any changes to my tank during those 24 hours except not feeding anything. Is a 0.03ppm increase per day in phosphate with no external charges normal? Would that indicate a dead fish or dying chaeto or would the phosphate increase be much larger in one of those scenarios?

I just added the GFO reactor after taking that test. I will test again in 24 hours to see what the GFO did.


New member
The rock is atleast 2 years old. I removed a large ~10" decorative shell which had fish waste and uneaten food inside. Hopefully that helps.

I would like to stay away from urchins as I read they can be bulldozers. I actually removed two large turbo snails because they kept knocking over frags. I've replaced them with a couple of scarlet red hermits (should have 5 ish now), and 3 trochus snails. I've always had 3 Caribbean Nassarius Snails in the sand. Also added about 15 dwarf cerith snails.
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New member
24 hour update after adding a GFO reactor but disturbing a shell full of waste:

My phosphate jumped to 0.44ppm after adding a GFO reactor BUT I also removed a large decorative shell which leaked fish waste and food into the tank while lifting it out. The shell itself probably held 0.5L to 1L of water. I think that caused the spike. The water exiting the reactor tested at 0.38ppm phosphate. Does that sound right or is my GFO depleted after 24 hours and it should be 0 even though the tank is 0.44ppm phosphate? I think I need to do an emergency water change.


New member

I replaced about 25% of the water in my tank. I also vacuumed the gravel and brushed the algae off the rocks in a bucket outside the tank. My phosphate decreased to 0.08ppm. How does that make sense? The Hanna checker said 0.44 ppm before the 25% water change. I would have only expected a 25% decline in phosphate. This is almost a 80% drop in phosphate. I'm relieved, but really?

I think that decorative shell that accumulate fish waste was the culprit. In addition to over feeding frozen mysis shrimp without a pre-rinse. That would explain why my phosphate was through the roof while my nitrates weren't too bad. My Nitrate is about 1.0ppm/2.5ppm now ( I have trouble distinguishing the difference on my salifert test)